Array structure of solder balls able to control collapse

ABSTRACT

A solder ball array type package structure is able to control collapse. The package includes a substrate, a carrier, a plurality of dies, a molding compound and a plurality of solder balls. The substrate has at least one active surface. Pads are located on the first surface of the substrate. The carrier has at least an active surface and a back surface opposite the active surface. A plurality of dies are located on the back surface and the active surface of the carrier. The dies arranged on the active surface are electrically connected to the carrier by flip chip technology. A molding compound encapsulates on the back surface of the carrier to cover the dies on the back surface of the carrier. Solder balls having a base material are provided on the active surface of the carrier in array. At least three solder balls coated with the base material having a high melting-temperature core are further provided in the periphery of the array. The carrier is arranged such that the active surface faces the first surface of the substrate to allow each solder ball correspond to the one of the pads, respectively.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an array structure of solder balls ableto control collapse, specifically, to an array structure of solder ballsfor a BGA package which can control collapse.

2. Description of the Related Art

Integrated circuits plays an important role in current daily life. Withincreasing development in electronics, electronic products havinghumanized operation and higher performance are available. Additionally,various products are designed such that the features such as lesserweight and compact size are provided for comfortable use. In thesemiconductor fabricating process, a semiconductor product having higherintegration is available because of mass production of the 0.18micrometer integrated circuit.

In general, the production of an integrated circuit (IC) includes threestages: silicon wafer production, semiconductor process and ICpackaging.

Owing to the design trend always tends to lighter, thinner, shorter andsmaller products, various technologies for packages have been developed.Many fine packages such as chip scale package (CSP), wafer level packageor multiple chip module (MCM) are manufactured. In device assembly, amulti-level PCB having higher density can be used to allow the ICpackage to be arranged on the PCB more compactly.

Because the device with more complex function is developed, the amountof input/output pads for an IC package increases. Owing to shrink thepackage size, it trends to layout the input/output pads in an areaarray. Ball grid array package is a typical and popular package usingarea array in input/output pads layout.

A flip chip technology is often used for a chip scale package. Sincebonding pads are arranged in area array, a chip is attached to a carrierthrough bumps, and solder balls are used to connect the carrier to asubstrate in the flip chip technology, the package size and signaltransmission path can be reduced. Among the current flip chip products,Ball Grid Array (BGA) package is a common one.

Referring to FIGS. 1A and 1B, cross-sectional views of a conventionalarea array type package structure are shown.

As shown in FIG. 1A, pads 104 are formed on a substrate 102 as junctionsfor external connection. A carrier 106 comprises at least an activesurface 101 and a plurality of solder balls 108 are provided thereon.

As shown in FIG. 1B, the solder balls 108 on the active surface of thecarrier 106 are attached to the pads 104 of the substrate 102,respectively. At the reflowing step, the eutectic solder balls 108 aremelted into solder and wetting to pads 104 of the substrate 102. As thearea 124 for wetting becomes larger, the level of collapse becomesserious. I.e., if the height 122 of the solder ball 108 is lowered, thestandoff between the carrier 106 and the substrate 102 is reduced. Incase of serious collapse, the standoff between the carrier 106 and thesubstrate 102 is so small that the adjacent solder balls 108 becomesshort to influence adversely the yield.

Some packages which require high accuracy for the standoff between thecarrier 106 and the substrate 102, such as cavity down BGA or packagehaving chips thereunder, usually result in low yield due to uncontrolledcollapse. The extremely small standoff between the carrier 106 and thesubstrate 102 generated from undue collapse often makes the solder ballstructure with solder joints bad and the endurance for the thermal cycleinsufficient.

Therefore, it is one object of the present invention to provide a solderball array type package structure in which the standoff between thecarrier and the substrate can be improved and the level of collapse canbe controlled.

It is another object of the present invention to provide a solder ballarray type package structure in which the reliability of solder jointcan be strengthened in thermal cycle.

It is still another object to provide a structure of solder ball arrayin which short connection to adjacent solder balls can be prevented andthe level of collapse can be controlled.

According to the present invention, a solder ball array type packagestructure able to control the collapse is provided, comprising at least:a substrate, a carrier, a plurality of dies, a molding compound and aplurality of solder balls. The substrate has a first surface. Pads areprovided on the first surface of the substrate. The carrier has at leastan active surface and a back surface opposite the active surface. Aplurality of dies are provided on the back surface and the activesurface of the carrier. The dies are arranged on the active surface byflip chip technology. A molding compound overlies on the back surface ofthe carrier to cover the dies on the back surface of the carrier. Solderballs including base material are provided on the active surface of thecarrier in array. In the periphery of the array are provided at leastthree solder balls, each further having a core of a high melting point(hereinafter, called as “high-melting-temperature” or “HMT” core). Thecarrier is arranged such that the active surface faces the first surfaceof the substrate to allow each solder ball correspond to one of thepads, respectively.

According to one preferred embodiment of the present invention, at leastthree solder balls further having a high-melting-temperature core areprovided in the periphery of the solder ball array structure of thepresent invention to control the collapse of the solder ball and thusensure the standoff between the carrier and the substrate. Theelectrical connection of the pads and solder balls on the substrate canbe achieved. During the reflowing process, the carrier is supported bythe solder balls having high-melting-temperature cores, so that thecollapse level is controlled. Then, the short situation of the adjacentsolder balls is prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the invention as claimed.

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciple of the invention. In the drawings,

FIGS. 1A and 1B are schematic, cross-sectional views of a conventionalflip chip type package structure;

FIGS. 2A and 2B are schematic, cross-sectional views of an solder ballarray type package structure able to control the collapse according tothe first embodiment of the present invention;

FIGS. 3A and 3B are schematic, cross-sectional views of a solder ballarray type package structure able to control the collapse according tothe second embodiment of the present invention; and

FIGS. 4A and 4B are schematic, cross-sectional views of a array typepackage structure able to control the collapse according to the thirdembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 2A and 2B, schematic, cross-sectional views of asolder ball array type package structure according to the firstembodiment of the present invention are shown.

As shown in FIG. 2A, a substrate 202, such as a Printed Circuit Board(PCB), comprises at least a first surface 205. Pads 204 constructed of amaterial such as copper are provided on a first surface 205 of thesubstrate 202. A carrier 206 comprises at least an active surface 201and a back surface 203 opposite the active surface 201. A first die 210is provided on the back surface 203 of the carrier 206. The first die210 is electrically connected to the back surface 203 of the carrier 206by wires 214. A second die 212 is provided on the active surface 201 ofthe carrier 206 and the second die 212 is electrically connected to thecarrier 206 by flip chip technology. A molding compound 216, such asepoxy, is encapsulated on the back surface 203 of the carrier 206 andthe first die 210 and the wires 214 thereon.

Solder balls 208 are provided on the active surface 201 of the carrier206 in array. The solder balls 208 includes at least one base material218. If the base material 218 is eutectic lead/tin alloy which of amelting point of 183° C., then the lead/tin ratio is about 37/63. Atleast three solder balls 208 a coated with a base material 218, eachhaving a high-melting-temperature core (HMT core) 220, are provided inthe periphery of the array. The HMT core 220 is made of lead-rich alloy,dummy ball, copper, lead/tin alloy or the like. For example, when theHMT core 220 is lead/tin alloy and its melting point is 240° C., theratio of lead to tin is about 90/10.

As shown in FIG. 2B, the carrier 206 is arranged such that the activesurface 201 faces the first surface 205 of the substrate 202 to alloweach solder ball 208 to correspond to one of the pads 204, respectively.Reflowing process is then carried out. Because the solder balls 208 madeof the base material 218 has a lower melting point than HMT cores 220 ofthe solder balls 208 a, the HMT cores 220 can maintain the distancebetween the carrier 206 and the substrate 202 and allow wetting of thesolder balls 208 and the pads 204 on the substrate 202 when the basematerial 208 starts to melt. Therefore, collapse can be controlled, thatis, the solder balls 208 have larger height 222 such that the structureof the solder balls 208 as a solder joint for the carrier 206 and thepads 204 has a better strength, hence, larger endurance for the thermalstress generated during the thermal cycle can be reached. The adjacentsolder balls 208 can be further prevented from being short, and theyield can thus be improved.

Referring to FIGS. 3A and 3B, schematic, cross-sectional views of solderball structure according to the second preferred embodiment of thepresent invention are shown.

As shown in FIG. 3A, a substrate 302 comprises at least a first surface305. Pads 304 are provided on the first surface 305 of the substrate302. A carrier 306 comprises at least an active surface 301 and a backsurface 303 opposite the active surface 301. A cavity down BGA comprisesat least a die 310, a plurality of wires 314, a molding compound 316 anda plurality of solder balls 308. A die 310 is provided on the activesurface 301 of the carrier 306 and electrically connected to the carrier306 by wires 314. A molding compound 316 is encapsulated on the activesurface 301 of the carrier 306. At least three solder balls coated witha base material 318 are further provided in the periphery of the array,each having HMT core 320.

As shown in FIG. 3B, the active surface 301 of the carrier 306 faces thefirst surface 305 of the substrate 302 to allow each solder ball 308 tocorrespond to the one of the pads 304, respectively. Reflowing is thencarried out. Because the solder balls 308 made of the base material 318has a lower melting point than HMT cores 320 of the solder balls 308 a,the HMT cores 320 can maintain the distance between the carrier 306 andthe substrate 302 and allow wetting of the solder balls 308 and the pads304 on the substrate 302 when the base material 318 starts to melt. Thecollapse can be under control by the solder balls 308 a, each having HMTcores 320 to avoid the molding compound 316 from contacting thesubstrate 302.

Referring to FIGS. 4A and 4B, schematic, cross-sectional views of asolder ball-type package structure that can control the collapse of thesolder ball according to the third embodiment of the present inventionare shown.

As shown in FIG. 4A, a substrate 402 comprises at least a first surface405. Pads 404 are provided on the first surface 405 of the substrate402. A carrier 406 comprises at least an active surface 401 and a backsurface 403 opposite the active surface 401. Dies 410 are provided onthe back surface 403 of the carrier 406 by flip chip technology. Amolding compound 416 encapsulates the back surface 403 of the carrier406 and the dies 410 thereon. Solder balls 408 are provided on theactive surface 401 of the carrier 406 in an array layout. Moreover, atleast three solder balls 408 a coated with the base material 418 arefurther provided in the periphery of the array, each having a HMT core420.

As shown in FIG. 4B, the carrier 406 is arranged such that the activesurface 401 faces the first surface 405 of the substrate 402 to alloweach solder ball 408 to correspond to the one of the pads 404,respectively. Reflowing process is then carried out. Because the solderballs 408 a made of the base material 418 has a lower melting point thanHMT core 420 of the solder balls 408 a, the HMT core 420 can maintainthe distance between the carrier 406 and the substrate 402 and allowwetting of the solder balls 408 and the pads 404 on the substrate 402when the base material 418 starts to melt. Therefore, the collapse ofthe solder balls 408 can be controlled by arrangement of at least threesolder balls 408 a having HMT cores 420. The adjacent solder balls 408can be further prevented from being short.

As mentioned above, a solder ball array type package structure able tocontrol the collapse of the solder ball according to the presentinvention provides the advantages as follows:

1. In the periphery of the solder ball array structure are provided atleast three solder balls, each having an HMT core, to control thecollapse of the solder ball and thus maintain the distance between thecarrier and the substrate.

2. The HMT cores can maintain the height for the eutectic solder ballsand provide sufficient strength of the solder joint during a thermalcycle.

3. During the reflowing process, the collapse of solder balls can becontrolled by arrangement the solder balls having HMT cores, such thatthe adjacent solder balls can be further prevented from being short.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the forgoing, it is intended that the present invention covermodification and variation of this invention provided they fall withinthe scope of the following claims and their equivalents.

What is claimed is:
 1. A solder ball array type package structure ableto control collapse, comprising at least: a substrate having at least afirst surface; a plurality of pads provided on the first surface of thesubstrate; a carrier having at least an active surface and a backsurface opposite the active surface; a molding compound encapsulatingthe back surface of the carrier and the dies thereon; and a plurality ofsolder balls each of which is made of a base material, wherein thesolder balls are arranged on the active surface of the carrier in array;at least three peripheral solder balls provided in the periphery of thearray, wherein each of peripheral solder balls is made of the basematerial with a high-melting-temperature core (HMT core) therein,wherein the carrier is arranged such that the active surface faces thefirst surface of the substrate to allow each solder ball correspond toone of the pads, respectively.
 2. The solder ball array type packagestructure able to control collapse of claim 1, wherein the base materialis eutectic lead/tin alloy.
 3. The solder ball array type packagestructure able to control collapse of claim 2, wherein the base materialis eutectic lead/tin alloy with a lead/tin ratio of about 37/63.
 4. Thesolder ball array type package structure able to control collapse ofclaim 1, wherein the HMT cores of the solder balls are made of amaterial selected from a group consisting of copper or high lead/tinalloy.
 5. The solder ball array type package structure able to controlcollapse of claim 4, wherein the HMT cores are high lead/tin alloy witha lead/tin ratio of about 90/10.
 6. The solder ball array type packagestructure able to control collapse of claim 1, wherein the melting pointof the base material is lower than that of the HMT core.
 7. The solderball array type package structure able to control collapse of claim 1,wherein the substrate is a printed circuit board.
 8. The solder ballarray type package structure able to control collapse of claim 1,wherein a material for the pads of the substrate is copper.
 9. A solderball array type package structure able to control collapse, comprisingat least: a substrate having at least a first surface; a plurality ofpads provided on the first surface of the substrate; a carrier having atleast an active surface and a back surface opposite the active surface;a plurality of dies provided on the active surface and the back surfaceof the carrier, wherein the dies arranged on the active surface of thecarrier are electrically connected to the carrier by flip chiptechnology; a molding compound encapsulating the back surface of thecarrier and the dies thereon; a plurality of solder balls each of whichis made of an eutectic base material, wherein the solder balls arearranged on the active surface of the carrier in array; and at leastthree peripheral solder balls provided in the periphery of the array,wherein each of the peripheral solder balls is made of the eutectic basematerial with a high-melting-temperature core therein, wherein thecarrier is arranged such that the active surface faces the first surfaceof the substrate to allow each solder ball correspond to one of thepads, respectively.